Node REPL that doesn't clobber _

console.js

var repl = require('repl')
var vm = require('vm');

var _;

var server = repl.start({
  eval: function (cmd, context, filename, callback) {
    try {
      var match = cmd.match(/^\((.*)\n\)$/);
      var code = match ? match[1] : cmd;
      context._ = _;
      var result = vm.runInThisContext(code, filename);
    } catch (error) {
      console.log(error.stack);
    } finally {
      _ = context._;
      callback(null, result);
    }
  }
}).on('exit', function () {
  process.exit(0);
});

I wrote this for myself because I wanted to load the app I'm working on in the REPL and run code, like you can do in Rails with rails console. But my app sets global._ = require('underscore'), so I don't have to manually require it in every source file, and the Node REPL was clobbering the _ variable.

This code snippet fixes the problem using the native Node repl and vm modules. It saves off the value of _ and restores it each time. Just invoke it like: node console.js

If you have an app and you want to pre-load a bunch of your classes into the global namespace for convenience, just do that here before the REPL is started.

Note one deficiency relative to just running node: You can't enter code that spans more than one line. You'll get a syntax error. Haven't figured that one out yet.